The launch team reports to the control center at NASA's Wallops Flight Facility.

T-minus 7 hours, 30 minutes

Complete Voice Checks

The launch team conducts voice checks over radio loops.

T-minus 6 hours, 30 minutes

Clear the Pad

Workers evacuate the launch pad.

T-minus 5 hours, 35 minutes

Poll to Initiate Fueling Sequence

The launch team conducts a "go/no go" poll to initiate the Antares fueling sequence.

T-minus 5 hours

Vehicle Power-Up

The Antares launch vehicle is powered on using an external power source.

T-minus 4 hours, 5 minutes

Poll to Initiate Pre-Launch Processing

The launch team is polled for a "go" to begin the pre-launch processing sequence.

T-minus 3 hours, 40 minutes

15-minute Hold

The countdown holds for 15 minutes.

T-minus 3 hours, 30 minutes

RF Transmitter Checks

The launch team tests the Antares rocket's radio transmitter, which will be the communications link between the vehicle and the ground during flight.

T-minus 3 hours, 5 minutes

Poll to Initiate LOX Chilldown

The launch team is a polled for a "go" to begin the liquid oxygen chilldown, which conditions the ground and vehicle propellant lines for loading of the cryogenic propellant, which is stored at a temperature of minus 298 degrees Fahrenheit.

T-minus 3 hours

Begin Liquid Oxygen Chilldown

The liquid oxygen chilldown sequence begins.

T-minus 2 hours, 48 minutes

FTS Testing

The Antares flight termination system, which would destroy the rocket if it flew off course during launch, is tested to ensure it is ready for launch.

T-minus 2 hours, 24 minutes

Enable Ordnance

The Antares rocket's pyrotechnic charges, which are used to separate the rocket's stages and other components in flight, are set to enable.

T-minus 1 hour, 45 minutes

15-minute Hold

The countdown holds for 15 minutes.

T-minus 1 hour, 30 minutes

Begin Propellant Loading

Liquid propellants are pumped into the Antares first stage through the base of the rocket. The 12.8-foot-diameter first stage, fabricated in Ukraine, holds 21,000 gallons of RP-1 kerosene and 41,000 gallons of liquid oxygen. The Antares second stage is fueled by solid propellants, which were loaded when the stage was built.

T-minus 25 minutes

Start of Engine Low-Flow Chilldown

The chilldown sequence for the Antares rocket's two AJ26 main engines begins to prepare the engines for ignition.

T-minus 10 minutes

Start of Engine Medium-Flow Chilldown

The chilldown sequence is transitioned to a medium flow.

T-minus 5 minutes

Transfer Avionics to Internal Power

The Antares rocket's avionics are switched to run off of an internal battery.

T-minus 3 minutes, 30 seconds

Initiate Terminal Countdown

The final three-and-a-half minutes of the countdown are run off a computer autosequence.

T-minus 2 minutes

Pressurize Propellant Tanks

The Antares rocket's first stage propellant tanks are pressurized for launch.

T-minus 15 seconds

Main Engine Slew Test

The Antares rocket's AJ26 first stage engines are slewed in a preflight steering check to ensure the gimbal system is ready for flight. The engines can gimbal up to 6 degrees from center to steer the rocket.

T-minus 5 seconds

TEL Retraction

The rocket's umbilical tower, which is also used to transport and erect the vehicle at the launch pad, is retracted away from the launch vehicle.

T-minus 0 seconds

Main Engine Ignition

The two AJ26 main engines ignite with the help of a start cartridge before ramping up to a combined thrust level of approximately 750,000 pounds.

T+plus 1.5 seconds

Engine Health Check Complete

A computer-controlled health check of the performance of the AJ16 engines is completed before liftoff.

T+plus 2 seconds

Liftoff

After the engines are confirmed healthy, the hold-down system releases the Antares rocket at liftoff.

Data source: Orbital Sciences Corp.

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